Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$75.61	8.865%	$82.3128	$82.31	$82.30	$82.30
Purchase #2	$216.69	10.337%	$239.0892	$239.09	$239.10	$239.10
Purchase #3	$189.61	13.449%	$215.1106	$215.11	$215.10	$215.10
Purchase #4	$135.40	11.421%	$150.864	$150.86	$150.85	$150.90
Purchase #5	$101.55	4.384%	$106.002	$106.00	$106.00	$106.00
Purchase #6	$209.91	7.171%	$224.9626	$224.96	$224.95	$225.00
Purchase #7	$18.87	13.229%	$21.3663	$21.37	$21.35	$21.40
7 purchase totals =	$947.64		$1,039.7075	$1,039.70	$1,039.65	$1,039.80